First remember that you cannot spot reduce bodyfat so if you're looking to get leaner you will have to improve your diet, continue training, and generally...drop your bodyfat level.
As for running, long distance running...as most aerobic activities...will definately slim the legs.
Specifically, when training legs most exercises can be used for endurance/definition...the key is to make sure you are doing sets of higher reps. I particualrly like lunges (forward, backward, and lateral) for shaping the legs and for developing the hamstring/glute tie-in. SLDL are also gr8, as are leg extensions and squats..just be sure to keep the reps in the 12-20 range...and IMHO...closer to 15-20.